SATURATED HIDROCARBONS

ALKANE

Alkane

= paraffin

= saturated hidrocarbons

= hydrocarbons with only single covalent bonds between the carbon atoms

Definition

Acyclic branched or unbranched hydrocarbons having the general formula CnH2n+2 , and therefore consisting entirely of hydrogen atoms and saturated carbon atoms.

IUPAC Gold Book

Sifat

Sukar bereaksi C1 – C4 pada tekanan & suhu normal fase gas

C5 – C17 pada tekanan & suhu normal fase cair

PC18 pada tekanan & suhu normal fase padat Mudah larut pada pelarut non polar Berat jenis naik dengan penambahan atom C Pada alkana rantai lurus semakin panjang

rantai maka titik didih & titik leleh semakin tinggi

Carbon Bonding in Alkane

Each carbon atom must have 4 bonds (either C–H or C–C bonds),

and each hydrogen atom must be joined to a carbon atom (H–C bonds).

Straight-chain alkanes are sometimes indicated by the prefix n- (for normal)

Name Molecular Formula CnH2n+2

Structural Formula

Methane CH4CH4

Ethane C2H6CH3–CH3

Propane C3H8CH3–CH2–CH3

Butane C4H10CH3–CH2–CH2–CH3

Pentane C5H12 CH3–CH2–CH2–CH2–CH3

Hexane C6H14CH3–CH2–CH2–CH2–CH2–CH3

Heptane C7H16CH3–CH2–CH2–CH2–CH2–CH2–CH3

Octane C8H18CH3–CH2–CH2–CH2–CH2–CH2–CH2–CH3

Nonane C9H20CH3–CH2–CH2–CH2–CH2–CH2–CH2–CH2–CH3

Decane C10H22CH3–CH2–CH2–CH2–CH2–CH2–CH2–CH2–CH2–CH3

Isomerism

Alkanes with more than three carbon atoms can be arranged in a multiple number of ways, forming different structural isomers.

Isomers are compounds that have the same molecular formula but different structural formulas.

College Chemistry_ch.21.8_p.529

Practice 1 :

Write structural formulas and

condensed structural formulas of :

1. Pentane C5H12

2. Hexane C6H14

Pentane

Hexane

AlkylNumber of carbons Molecule name

1 methyl2 ethyl3 propyl4 butyl5 pentyl/amyl6 hexyl7 heptyl8 octyl9 nonyl10 decyl11 undecyl12 dodecyl

Isopropyl

Isobutyl

sec-Butyl

tert-Butyl

IUPAC Nomenclature : Basic Principles (1)Select the longest continuous chain of carbon

atoms as the parent compound, and consider all alkyl groups attached to it as side chains that have replaced hydrogen atoms of the parents hydrocarbon.

The name of the alkane consists of the name of the parent compound prefixed by the names of the side-chain alkyl groups attached to it.

IUPAC Nomenclature : Basic Principles (2)Number the carbon atoms in the parent carbon

chain starting from the end closest to the first carbon atom that has an alkyl or other group substitued for a hydrogen atom.

IUPAC Nomenclature : Basic Principles (3)Name each side-chain alkyl group and

designate its position on the parent carbon chain by a number (for example, 2-methyl means a methyl group attached to carbon number 2).

IUPAC Nomenclature : Basic Principles (4)When the same alkyl-group side chain occurs

more than once, indicate this by a prefix (di-, tri-, tetra-, and si forth) written in front of the alkyl-group name (for example, dimethyl indicates two methyl groups).

The numbers indicating the positions of these alkyl groups are separated by a comma and followed by a hypen and are placed in front of the name (for example, 2,3-dimethyl).

IUPAC Nomenclature : Basic Principles (5)When several different alkyl groups are

attached to the parent compound, list them in alphabetical order; for example, ethyl before methyl in 3-ethyl-4-methyloctane.

College Chemistry_ch.21.9_p.533

Practice 2 :

The following names are incorrect. Tell why the name is wrong and gave the correct name.

1. 3-methylbutane

2. 2-ethylbutane

3. 2-dimethylpentane

4. 3-methyl-5-ethyloctane

5. 3,5,5-triethylhexane

1. 3-methylbutane

CH3 – CH2 – CH – CH3

CH3

2-methylbutane

2. 2-ethylbutane

CH3 – CH2 – CH – CH3

CH2

CH3

3-methylpentane

3. 2-dimethylpentane

CH3

CH3 – CH – CH – CH2 – CH3

CH3

2,2-dimethylpentane

4. 3-methyl-5-ethyloctaneCH3 – CH2 – CH – CH2 – CH – CH2 – CH2 – CH3

CH3 CH2

CH3

5-ethyl-3-methyloctane

5. 3,5,5-triethylhexane

CH2

CH3

CH3 – CH2 – CH – CH2 – C – CH3

CH2 CH2

CH3 CH3

3,5-diethyl-3-methylheptane

Reaction of Alkane :Halogenation

Halogenation means substitution of halogens for hydrogen.

RH + X2 RX + HX

X = F, Cl, Br, I

Example :

CH3CH3 + Cl2 CH3CH2Cl + HCl

chloroethane

Reaction of Alkane :Dehydrogenation

Dehydrogenation means removal of hydrogen.

CnH2n+2 700 – 900 oC CnH2n + H2

Example :

CH3CH2CH3 CH3CH=CH2 + H2

propene

Reaction of Alkane :Cracking

Cracking means breaking up large molecules to form smaller ones.

Example :

C16H34 C8H18 + C8H16

alkane alkane alkene

Reaction of Alkane :Isomerization

Isomerization means rearrangement of molecular structures.

Example :

Chlorination Products of Methane(1)

CH4 + Cl2 CH3Cl

CH3Cl + Cl2 CH2Cl2

CH2Cl2 + Cl2 CHCl3

CHCl3 + Cl2 CCl4 + HCl

Chlorination Products of Methane(2)Formula IUPAC name Common name

CH3Cl Chloromethane Methyl chloryde

CH2Cl2 Dichloromethane Methylene chloryde

CHCl3 Trichloromethane Chloroform

CCl4 Tetrachloromethane Carbon tetrachloride

Cycloalkane/cycloparaffin/naphtane Cycloalkanes are types of alkanes which

have one or more rings of carbon atoms in the chemical structure of their molecules struktur alisiklik.

Rumus: CnH2n

Contoh:

Cyclopropane Cyclobutane CyclopentaneCyclohexane

C3H6 C4H8 C5H10 C6H12

Sources of Alkanes

The two main sources of alkanes are natural gas and petroleum / crude oil.

Natural gas consists of : Methane Other hydrocarbons Hydrogen Nitrogen Carbon monoxide Carbon dioxide Hydrogen sulfide (just in some location)

Petroleum is formed by the decomposition of plants and animals over million of years.

Composition: Carbon Hydrogen Nitrogen Oxygen Sulfur MetalsFour different types of hydrocarbon molecules appear

in crude oil : Paraffins Naphthenes Aromatics Asphaltics

Fractional Distillation of Crude Oil

Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractional column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units.

Octane Rating

Octane CH3(CH2)6CH3

Octane has 18 structural isomers :• Octane (n-octane) 0• 2-Methylheptane• 3-Methylheptane• 4-Methylheptane• 3-Ethylhexane• 2,2-Dimethylhexane• 2,3-Dimethylhexane• 2,4-Dimethylhexane• 2,5-Dimethylhexane• 3,3-Dimethylhexane• 3,4-Dimethylhexane• 2-Methyl-3-ethylpentane• 3-Methyl-3-ethylpentane• 2,2,3-Trimethylpentane• 2,2,4-Trimethylpentane (isooctane) 100• 2,3,3-Trimethylpentane• 2,3,4-Trimethylpentane• 2,2,3,3-Tetramethylbutane

The octane rating was developed by chemist Russel Marker at the Ethyl Corporation at 1926. The selection of n-heptane as the zero point of the scale was due to the availability of very high purity n-heptane, not mixed with other isomers of heptane or octane, distilled from the resin of the Jeffrey Pine. Other sources of heptane produced from crude oil contain a mixture of different isomers with greatly differing ratings, which would not give a precise zero point.Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause detonation.

The alternative method to boost octane rating and minimize engine knocking is too add small amounts of an additive to the fuel. One such additive commonly used in gasoline was tetraethyllead, (C2H5)4Pb.

The function of tetraethyllead is to prevent the premature explosions that constitute knocking.

Use of tetraetthyllead additives poses a serious enviromental hazard. Lead becomes pollutant in air, water, and sovent.

Current additives in anleaded gasoline : • Toluene• Xylene• Methyl tert-butyl ether (MTBE)